1. Field of the Invention
The present invention relates to a heating apparatus for curing a film coated on a surface of a workpiece such as a semiconductor wafer, a glass substrate, or the like.
2. Description of the Relevant Art
It has been customary to deposit a film of phosphosilicate glass (PSG) or boron silicate glass (BPSG), or a nitride film on a semiconductor wafer, or to deposit a film of silicon dioxide (SiO.sub.2) on a glass substrate by first coating the surface of the semiconductor wafer or glass substrate with a coating solution of the above material and thereafter curing the coated semiconductor wafer or glass substrate with a heating device.
Heretofore, the heating device comprises a reaction chamber fixedly mounted on a base plate, a heater disposed around the reaction chamber, and a holder for holding a number of workpieces to be cured, the holder being insertable into the reaction chamber from below. In operation, the reaction chamber is evacuated to allow a solvent in the films coated on the workpieces to evaporate away, and then the workpieces are heated for curing.
The holder with a plurality of workpieces maintained therein is lifted into the reaction chamber before a curing process, and then lowered out of the reaction chamber after the curing process. Since the holder is vertically moved into and out of the reaction chamber at low speed, the overall time required to process the workpieces is lengthy.
Furthermore, the reaction chamber and heater are relatively positioned in fixed relationship. Consequently, once the temperature in the reaction chamber has increased as a result of the heating process, it does not drop quickly. When a next batch of workpieces is set in the reaction chamber and the reaction chamber is evaporated to remove the solvent by way of evaporation, a condensation reaction occurs at the same time, tending to develop cracks in the coated films.